HiRISE images

A piece of Mars: Bright dunes once marched through the depression created by a double impact. How can you tell the dunes are no longer moving? Because one of them has its own little crater sitting on it. A mobile dune would quickly erase such a distinctive feature. (HiRISE ESP_027018_1925) read more ❯

A piece of Mars: When the wind sandblasts at layered rocks, some pretty swirly patterns emerge. These are flat layers that take on a stacked wedding-cake appearance on an outcrop elongated by the wind. The direction of the stacks indicates the direction of the wind -- from upper left to lower right. (ESP_027011_1735) read more ❯

A piece of Mars: Wind streaks are a common sight on Mars. They are formed either by the wind blowing stuff away or blowing stuff in, and it can be quite difficult to tell which is which. In this case, I'm not entirely sure -- I suspect the bright orange streaks are erosional and the darker ones are depositional. The pale pink ones are a mystery to me. Regardless of how they form, they certainly indicate winds have blown from the lower right to upper left. (HiRISE ESP_027007_1690) read more ❯

A piece of Mars: Most of the image, stretching beyond the edges of this frame, shows a bland gray landscape of lava blanketed in dust. But one small patch of blue shows where sand is still actively moving and piling up. As usual, it's in the lee of a topographic feature. (HiRISE ESP_027002_1765) read more ❯

A piece of Mars: What makes a dune different from a random pile of sand? Usually the requirement is that it has a "slipface", a steep avalanching slope. The central dune in the image here has a small one, making it a type of dune called a barchan. The other dunes are called "dome dunes", because they don't have proper slip faces. It is arguable that they aren't really proper dunes at all. (HiRISE ESP_027378_2540) read more ❯

A piece of Mars: Dunes near the north pole of Mars form in a very cold environment. Winter ice continually tries to stop them in their tracks, which makes for unusually rounded dunes like these. (HiRISE ESP_027451_2635) read more ❯

A piece of Mars: What an intriguing mess this is. These are dunes or ripples, oriented every which way, and mottled with white spots. The different orientations tell us that the winds blow from several different directions, on timescales long enough to seriously influence the dunes. The mottling is a mystery. (HiRISE ESP_025386_1800) read more ❯

A piece of Mars: Way up in the cold northern plains of Mars, some of the dunes are being blown away slowly by the wind. Here are some that are barely there yet -- dark patches of sand in the shape of their former glory. (HiRISE ESP_027389_2645) read more ❯

A piece of Mars: The thin stripes within stripes are the bones of dunes. You're seeing old dunes that have had their tops eroded away so you're seeing into their insides, as if you were dissecting them in a biology class and looking at their skeletons. That's unusual -- on Earth dunes usually get buried or destroyed, so being able to see their interior structure is quite amazing. (HiRISE ESP_026992_2025) read more ❯

A piece of Mars: This is the edge of the northern polar cap on Mars. At the top is the bright icy surface, which is abruptly cut by a cliff. The wall of the cliff shows many layers of different materials -- the darker ones are old dunes. How cool is it to know that the polar ice cap on another planet is sitting on what used to be an enormous sand sea? It's like looking at limestone and shale on mountains here on Earth an imagining them once being at the bottom of an ocean. It blows my mind.... read more ❯